Irida-β-ketoimines Derived from Hydrazines To Afford Metallapyrazoles or N–N Bond Cleavage: A Missing Metallacycle Disclosed by a Theoretical and Experimental Study

Unprecedented metallapyrazoles [IrH 2 {Ph 2 P(o-C 6 H 4 )CNNHC(o-C 6 H 4 )PPh 2 }] (3) and [IrHCl{Ph 2 P(o-C 6 H 4 )CNNHC(o-C 6 H 4 )PPh 2 }] (4) were obtained by the reaction of the irida-β-ketoimine [IrHCl{(PPh 2 (o-C 6 H 4 CO))(PPh 2 (o-C 6 H 4 CNNH 2 ))H}] (2) in MeOH heated at reflux in the presence and absence of KOH, respectively. In solution, iridapyrazole 3 undergoes a dynamic process due to prototropic tautomerism with an experimental barrier for the exchange of ΔG coal ⧧ = 53.7 kJ mol -1 . DFT calculations agreed with an intrapyrazole proton transfer process assisted by two water molecules (ΔG = 63.1 kJ mol -1 ). An X-ray diffraction study on 4 indicated electron delocalization in the iridapyrazole ring. The reaction of the irida-β-diketone [IrHCl{(PPh 2 (o-C 6 H 4 CO)) 2 H}] (1) with H 2 NNRR' in aprotic solvents gave irida-β-ketoimines [IrHCl{(PPh 2 (o-C 6 H 4 CO))(PPh 2 (o-C 6 H 4 CNNRR'))H}] (R = R' = Me (5); R = H, R' = Ph (8)), which can undergo N-N bond cleavage to afford the acyl-amide complex [IrHCl(PPh 2 (o-C 6 H 4 CO))(PPh 2 (o-C 6 H 4 C(O)N(CH 3 ) 2 ))-κP,κO] (6) or [IrHCl(PPh 2 (o-C 6 H 4 CO))(PPh 2 (o-C 6 H 4 CN)-κP)(NH 2 NHPh-κNH 2 )] (9) containing o-(diphenylphosphine)benzonitrile and phenylhydrazine, respectively. From a CH 2 Cl 2 /CH 3 OH solution of 9 kept at -18 °C, single crystals of [IrHCl(PPh 2 (o-C 6 H 4 CO))(PPh 2 (o-C 6 H 4 CN)-κP))(HN═NPh-κNH)] (10) containing o-(diphenylphosphine)benzonitrile and phenyldiazene were formed, as shown by X-ray diffraction. The reaction of 1 with methylhydrazine in methanol gave the hydrazine complex [IrCl(PPh 2 (o-C 6 H 4 CO)) 2 (NH 2 NH(CH 3 )-κNH 2 )] (7). Single-crystal X-ray diffraction analysis was performed on 6 and 7.